Fix nexttoward overflow in non-default rounding modes (bug 19059).

ISO C requires overflowing results from nexttoward to be the
appropriate infinity independent of the rounding mode, but some
implementations use a rounding-mode-dependent result (this is the same
issue as was fixed for nextafter in bug 16677).  This patch fixes the
problem by making the nexttoward implementations discard the result
from the floating-point computation that forced an overflow exception
and then return the infinity previously computed with integer
arithmetic.

Tested for x86_64, x86, mips64 and powerpc.

	[BZ #19059]
	* math/s_nexttowardf.c (__nexttowardf): Do not return value from
	overflowing computation.
	* sysdeps/i386/fpu/s_nexttoward.c (__nexttoward): Likewise.
	* sysdeps/i386/fpu/s_nexttowardf.c (__nexttowardf): Likewise.
	* sysdeps/ieee754/ldbl-128/s_nexttoward.c (__nexttoward):
	Likewise.
	* sysdeps/ieee754/ldbl-128/s_nexttowardf.c (__nexttowardf):
	Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c (__nexttoward):
	Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c (__nexttowardf):
	Likewise.
	* sysdeps/ieee754/ldbl-96/s_nexttoward.c (__nexttoward): Likewise.
	* sysdeps/ieee754/ldbl-96/s_nexttowardf.c (__nexttowardf):
	Likewise.
	* sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c (__nldbl_nexttowardf):
	Likewise.
	* math/libm-test.inc (nexttoward_test_data): Add more tests.

7 files changed, 16 insertions, 13 deletions

diff --git a/sysdeps/ieee754/ldbl-128/s_nexttoward.c b/sysdeps/ieee754/ldbl-128/s_nexttoward.c
index e62ca3fef8..2ee7a1be5c 100644
--- a/sysdeps/ieee754/ldbl-128/s_nexttoward.c
+++ b/sysdeps/ieee754/ldbl-128/s_nexttoward.c
@@ -73,8 +73,8 @@ double __nexttoward(double x, long double y)
 	}
 	hy = hx&0x7ff00000;
 	if(hy>=0x7ff00000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  double u = x+x;			/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00100000) {
 	    double u = x*x;			/* underflow */
diff --git a/sysdeps/ieee754/ldbl-128/s_nexttowardf.c b/sysdeps/ieee754/ldbl-128/s_nexttowardf.c
index ccd49d235d..9c9c7e5283 100644
--- a/sysdeps/ieee754/ldbl-128/s_nexttowardf.c
+++ b/sysdeps/ieee754/ldbl-128/s_nexttowardf.c
@@ -59,7 +59,10 @@ float __nexttowardf(float x, long double y)
 	    }
 	}
 	hy = hx&0x7f800000;
-	if(hy>=0x7f800000) return x+x;	/* overflow  */
+	if(hy>=0x7f800000) {
+	  float u = x+x;		/* overflow  */
+	  math_force_eval (u);
+	}
 	if(hy<0x00800000) {
 	    float u = x*x;		/* underflow */
 	    math_force_eval (u);	/* raise underflow flag */
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c b/sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c
index 85140c1d02..8c6119825e 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c
@@ -74,8 +74,8 @@ double __nexttoward(double x, long double y)
 	}
 	hy = hx&0x7ff00000;
 	if(hy>=0x7ff00000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  double u = x+x;			/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00100000) {
 	    double u = x*x;			/* underflow */
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c b/sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c
index b27f0bb380..4000a93e69 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c
@@ -63,8 +63,8 @@ float __nexttowardf(float x, long double y)
 	}
 	hy = hx&0x7f800000;
 	if(hy>=0x7f800000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  float u = x+x;		/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00800000) {		/* underflow */
 	    float u = x*x;
diff --git a/sysdeps/ieee754/ldbl-96/s_nexttoward.c b/sysdeps/ieee754/ldbl-96/s_nexttoward.c
index b972a3eb3a..7908f9c0ff 100644
--- a/sysdeps/ieee754/ldbl-96/s_nexttoward.c
+++ b/sysdeps/ieee754/ldbl-96/s_nexttoward.c
@@ -70,8 +70,8 @@ double __nexttoward(double x, long double y)
 	}
 	hy = hx&0x7ff00000;
 	if(hy>=0x7ff00000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  double u = x+x;			/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00100000) {
 	    double u = x*x;			/* underflow */
diff --git a/sysdeps/ieee754/ldbl-96/s_nexttowardf.c b/sysdeps/ieee754/ldbl-96/s_nexttowardf.c
index f1fe4e7ca7..53c527d9ac 100644
--- a/sysdeps/ieee754/ldbl-96/s_nexttowardf.c
+++ b/sysdeps/ieee754/ldbl-96/s_nexttowardf.c
@@ -58,8 +58,8 @@ float __nexttowardf(float x, long double y)
 	}
 	hy = hx&0x7f800000;
 	if(hy>=0x7f800000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  float u = x+x;			/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00800000) {
 	    float u = x*x;			/* underflow */
diff --git a/sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c b/sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c
index 782e1a3340..dbcf840f2c 100644
--- a/sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c
+++ b/sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c
@@ -62,8 +62,8 @@ float __nldbl_nexttowardf(float x, double y)
 	}
 	hy = hx&0x7f800000;
 	if(hy>=0x7f800000) {
-	  x = math_narrow_eval (x+x);	/* overflow  */
-	  return x;
+	  float u = x+x;			/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00800000) {
 	    float u = x*x;			/* underflow */